from tkinter import *

master=Tk()

v1=StringVar()
v2=StringVar()
v3=StringVar()

def test(content):
    return content.isdigit()


testCMD=master.register(test)
e1=Entry(master,textvariable=v1,validate="key",validatecommand=(testCMD,'%p')).grid(row=0,column=0)

Label(master,text="+").grid(row=0,column=1)

e2=Entry(master,textvariable=v2,validate="key",validatecommand=(testCMD,'%p')).grid(row=0,column=2)

Label(master,text="=").grid(row=0,column=3)

e3=Entry(master,textvariable=v3,state="readonly").grid(row=0,column=4)

def calc():
    result=int(v1.get())+int(v2.get())
    v3.set(str(result))

Button(master,text="计算结果",command=calc).grid(row=1,column=2)

mainloop()
